New York City has thousands of police surveillance cameras, which really come in handy when a terrorist strikes. After the car bomb attempt last weekend, they captured an image of the vehicle driving through Times Square and one of a guy taking off his shirt who looked nothing like the guy arrested Monday.
Which raises the question: What good are cameras? The debate over them is often framed as hardheaded law enforcement types versus wimpy civil libertarians. Whether the cameras actually work in practice to help solve and prevent crime generally gets ignored.
It shouldn't. Leave aside those airy privacy concerns for the moment. Installing, maintaining and monitoring thousands of these devices, as in New York and Chicago, costs millions of dollars. Absent cameras, that money could be spent on beat cops, patrol cars, forensic equipment, jail cells, you name it.
The point of any law enforcement tool is not just to do some good but also to do some good at a reasonable cost compared with the alternatives. It's by no means clear that surveillance cameras even come close to meeting that standard.
There are some famous examples where they have helped identify criminals -- as in the July 21, 2005, subway bombing attempt in London, when video footage quickly led police to four conspirators. But a few cases, or even a few dozen, don't prove much.
A more complete assessment indicates that when it comes to preventing and solving crimes, the cameras are about as useful as a pet rock. Britain has 4 million of them, but a 2005 report by the British government found little evidence to justify the effort. Video surveillance, it said, "produced no overall effect" on crime.
In San Francisco, cameras significantly reduced property crime while having no effect on violent crime, drug dealing, prostitution or vandalism. So take comfort: When a mugger knocks you over the head, he won't steal your hubcaps.
But if cameras generally don't do much to prevent crime, surely they help collar the criminals they fail to deter? Not very often. A review by the London police department calculated, "For every 1,000 cameras in London, less than one crime is solved per year." Average cost for cracking a case: $30,000.
Chicago police say the cameras have produced 4,000 arrests since 2006. That sounds like a lot, but it works out to only about 1 in 200 arrests. And for 10,000 cameras, 4,000 arrests is not really a spectacular haul.